Release film for semiconductor resin molds

ABSTRACT

To provide a release film which has an extremely low gas permeability, an enormously small mold contamination by a mold resin and a high releasability. 
     A gas barrier release film for semiconductor resin molds, comprising a release layer (I) having excellent releasability, a plastic support layer (II) supporting the release layer, and a gas restraint layer (III) made of a metal or a metal oxide, formed between the release layer and the support layer, and having a xylene gas permeability of at most 10 −15  (kmol m/(s·m 2 ·kPa)) at 170° C. The release layer (I) is preferably formed from a fluororesin such as an ethylene/tetrafluoroethylene copolymer, and a metal oxide layer is preferably a layer of an oxide such as an aluminum oxide, a silicon oxide or a magnesium oxide.

TECHNICAL FIELD

The present invention relates to a release film for semiconductor resinmolds, particularly a release film for semiconductor resin molds whichcan reduce mold contamination.

BACKGROUND ART

A semiconductor element (chip) is usually, for protection and blockingfrom an external environment (such as external air, contaminant, light,magnetism, high frequency wave or impulse), sealed with a resin (moldresin) and is mounted, on a substrate, in the form of a semiconductorpackage having the chip accommodated therein. Typically, the package isone formed by a transfer molding wherein a thermosetting resin (moldresin) such as an epoxy resin is melted by heating, and then, it istransferred in a mold where the semiconductor chip is set, followed byfilling and curing. To the mold resin, a releasing agent is added inaddition to a curing agent, a curing accelerator and a filler, to securesmooth releasability of the formed package from the mold.

On the other hand, along with a strong demand for improvement ofproductivity of a semiconductor package, there is a problem such thatsince the resin adheres to the mold, the contaminated mold needs to beoften cleaned, or when a sealing resin having a low shrinkagecorresponding to a large package is used, sufficient releasabilitycannot be obtained even if a releasing agent is added. Therefore, therehas been a development made for a technique using a release film forresin molds (hereinafter referred to simply as a “release film”),wherein a semiconductor package is formed by injecting the resin intothe mold in such a state that the resin molding portion (cavity surface)of the mold is covered with the release film without directly contactingthe sealing resin to the cavity surface of the mold, and such techniquehas shown results of a certain level (e.g. Patent Documents 1 to 3).

However, recently, the mold resin to be used for a package of asemiconductor element is required to be changed to a non halogenatedmold resin for environmental protection. Further, in order to meet therequirements for forming a semiconductor into a fine pitch model, slimmodel, multilayer chip package model or LED, there has been a furtherprogress in forming a low viscosity mold resin or forming a mold resininto a liquid form resin. As a result, in the step of molding a resinfor the semiconductor element, the amount of gas and low viscositymaterial formed from the molten mold resin under a high temperatureenvironment increases, and the gas and low viscosity material permeatingthrough the above release film for molds contact the mold having a hightemperature, whereby the mold contamination becomes intense.

Further, covering the mold surface with the release film is carried outby sucking and supporting the film thereon under vacuum, but a volatilecomponent such as an oligomer in the film transfers to the covered sideof the mold, whereby the mold contamination may sometimes be caused.

Thus, even though the release film is used in such a manner, the side ofthe mold covered with the film, tends to be easily contaminated.Further, once the contamination is caused, the molding step for thesemiconductor is required to be stopped for cleaning, and such leads toa problem such that the production efficiency of the semiconductordecreases.

Further, from such a viewpoint, the above Patent Documents 1 and 2describe that in order to reduce the permeation of contaminants, avapor-deposited layer of a metal or a metal oxide is formed on one side(a surface to be contacted with a mold surface) of the release film.However, such a metal deposited layer is one to be used by directphysical contact to the mold surface, and a metal powder tends to bereleased from the film surface or a broken section of the film, wherebyits use for a molding step of the semiconductor resin is limited.

Further, in Patent Documents 1 and 2, the gas permeability of therelease film is defined by a permeation of carbon dioxide gas, but suchis not valid as an index for evaluating the permeability of a lowviscosity material, etc. from a resin, etc.

Further, the release film is now required to have higher releasabilityfrom the mold resin, but such was not considered for the above releasefilm, and the releasability was insufficient.

Further, in a case where a mold having a large surface roughness wasused, when the release film is vacuum sucked to the mold before resinsealing, the release film was sometimes required to have a moldobsequence property whereby the release film is capable of beingsufficiently stretched along the circumference length corresponding tothe surface roughness of the mold.

Patent Document 1: JP-A-2002-361643 (claims 1 to 3)

Patent Document 2: JP-A-2004-79566 (claims 1 to 3)

Patent Document 3: JP-A-2001-250838 (claims 1 to 6)

DISCLOSURE OF THE INVENTION Objects to be Accomplished by the Invention

An object of the present invention is to provide a release film which isstrongly demanded under the above circumstances, and which has extremelylow gas permeability as compared with conventional ones and cansubstantially prevent mold contamination by a mold resin.

Another object of the present invention is to define a gas permeabilityrequired for a release film to effectively suppress the moldcontamination, by using a gas permeability rate which is morerealistically corresponding to a low viscosity material from a resin asa mold contaminant.

A further object of the present invention is to provide a release filmhaving higher releasability from a mold resin.

Means to Accomplish the Objects

According to the present invention, the following laminate having anadhesive layer may be provided.

(1) A gas barrier release film for semiconductor resin molds, comprisinga release layer (I) having excellent releasability, a plastic supportlayer (II) supporting the release layer, and a gas restraint layer (III)made of a metal or a metal oxide, formed between the release layer andthe support layer, and having a xylene gas permeability of at most 10⁻¹⁵(kmol·m/(s·m²·kPa)) at 170° C.

(2) The release film according to the above (1), wherein the aboverelease layer (I) is formed from a fluororesin.

(3) The release film according to the above (2), wherein the abovefluororesin is an ethylene/tetrafluoroethylene copolymer.

(4) The release film according to any one of the above (1) to (3),wherein the plastic support layer (II) has a stress at a 200% elongationof from 1 MPa to 100 MPa at 170° C.

(5) The release film according to any one of the above (1) to (4),wherein the plastic support layer (II) is formed from an ethylene/vinylalcohol copolymer.

(6) The release film according to any one of the above (1) to (5),wherein the gas restraint layer (III) is formed on the plastic supportlayer (II).

(7) The release film according to any one of the above (1) to (6),wherein the gas restraint layer (III) is a layer of at least one oxideselected from a group consisting of aluminum oxide, silicon oxide andmagnesium oxide.

(8) The release film according to any one of the above (1) to (6),wherein the gas restraint layer (III) is a layer of at least one metalselected from a group consisting of aluminum, tin, chrome or stainlesssteel.

(9) The release film according to any one of the above (1) to (8),wherein a resin protection layer (III′) is formed on the gas restraintlayer (III).

(10) The release film according to any one of the above (1) to (9),wherein at least one surface of the mold release film is satin-finished.

EFFECTS OF THE INVENTION

According to the present invention, a release film can be provided whichhas extremely low gas permeability as compared with conventional onesand can substantially prevent mold contamination by a mold resin.Further, a gas permeability required for the release film to effectivelysuppress the mold contamination, is defined by a gas permeability ratecorresponding more realistically to a low viscosity material from aresin as a mold contaminant. Further, according to the presentinvention, a release film having a higher releasability from a moldresin can be provided. Further, the release film of the presentinvention is excellent in mold obsequence property.

Therefore, by using the release film of the present invention in amolding step of the semiconductor resin, mold contamination is extremelylow, and the number of times of mold cleaning can be reducedsubstantially, whereby it is possible to remarkably improve theproduction efficiency for molding a resin of a semiconductor element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a layer structure of a gasbarrier release film of the present invention.

FIG. 2 is a cross-sectional view illustrating a layer structure of a gasbarrier release film of the present invention.

FIG. 3 is a cross-sectional view illustrating a layer structure of a gasbarrier release film of the present invention.

FIG. 4 is a cross-sectional view illustrating a layer structure of a gasbarrier release film of the present invention.

FIG. 5 is a cross-sectional view illustrating a layer structure of a gasbarrier release film of the present invention.

FIG. 6 is a cross-sectional view illustrating a layer structure of a gasbarrier release film of the present invention.

MEANINGS OF SYMBOLS

-   -   1: Gas barrier release film    -   I: Release layer    -   II: Plastic support layer    -   III: Gas restraint layer (gas permeation suppressing layer) such        as metal oxide-deposited layer    -   III′: Resin protection layer

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be described in detail.

As shown in FIG. 1, the release film 1 for semiconductor resin molds ofthe present invention comprises at least a release layer (I) excellentin releasability and a plastic support layer (II) supporting the releaselayer, and it has a layer structure such that a gas restraint layer(III) made of a metal or a metal oxide is formed between the releaselayer and the support layer, and also has a xylene gas permeability ofat most 10⁻¹⁵ (kmol·m/(s·m²·kPa)) at 170° C.

Release Layer (I)

The release layer (I) in the release film of the present invention is alayer which is disposed to face a surface of the semiconductor elementto be sealed, and which is a layer to be contacted with a mold resininjected in a mold. It is also a layer to impart a sufficientreleasability from a cured mold resin.

A resin to form the release layer is not particularly limited as long asit is one having a releasability from a mold resin such as an epoxyresin, but the release layer is preferably formed from a fluororesinhaving particularly excellent releasability.

The fluororesin may, for example, be an ethylene/tetrafluoroethylenecopolymer (hereinafter referred to as “ETFE”), a chlorotrifluoroethyleneresin (hereinafter referred to as “CTFE”), a polytetrafluoroethylene(hereinafter referred to as “PTFE”), a vinylidene fluoride resin(hereinafter referred to as “VdF”), a vinyl fluoride resin (hereinafterreferred to as “VF”), a tetrafluoroethylene/hexafluoropropylenecopolymer (hereinafter referred to as “FEP”), atetrafluoroethylene/perfluoro(propyl vinyl ether) copolymer (hereinafterreferred to as “PFA”), a tetrafluoroethylene/vinylidene fluoridecopolymer or a combination of such resins. Preferred are ETFE, PTFE, FEPand PFA, and more preferred is ETFE. Further, ETFE may contain repeatingunits derived from at least one type of other monomers within a rangenot to impair its essential characteristics of imparting areleasability. Other monomers may, for example, be an α-olefin such aspropylene or butene; a compound represented by CH₂═CX(CF₂)_(n)Y (whereineach of X and Y is independently an hydrogen or fluorine atom, and n isan integer of from 1 to 8); a fluoroolefin having an hydrogen atom in anunsaturated group, such as vinylidene fluoride, vinyl fluoride,difluoroethylene (DFE), trifluoroethylene (TFE), pentafluoropropylene(PFP) or hexafluoroisobutylene (HFIB); and a fluoroolefin having nohydrogen atom in an unsaturated group, such as hexafluoropropylene(HFP), chlorotrifluoroethylene (CTFE), perfluoro(methyl vinyl ether)(PMVE), perfluoro(ethyl vinyl ether) (PEVE), perfluoro(propyl vinylether) (PPVE), perfluoro(butyl vinyl ether) (PBVE) or otherperfluoro(alkyl vinyl ether) (PAVE). Such other monomers may be usedalone or in combination as a mixture of two or more of them.

In the release film 1 of the present invention, as shown in FIG. 1, therelease layer (I) is supported by the plastic support layer (II) havingnecessary stiffness, whereby the thickness of the release layer may beas thin as just enough to impart a releasability. Usually, the thicknessis from 3 to 75 μm, preferably from 6 to 30 μm. Further, in FIG. 1,(III) is a gas restraint layer, which will be described later.

Further, as shown in FIG. 2, in the release film, the surface of therelease layer (I) to be laminated and adhered on the gas restraint layer(III), facing the support layer (II), is preferably surface-treated by acommon method to improve the adhesion. The surface-treating method may,for example, be a known corona discharge treatment in air, coronadischarge treatment in the presence of an organic compound, plasmadischarge treatment in the presence of an organic compound or dischargetreatment in a gas mixture of inert gas, polymerizable unsaturatedcompound gas and hydrocarbon oxide gas, and it is particularlypreferably the corona discharge treatment in air.

Plastic Support Layer (II)

The plastic support layer (II) in the release film of the presentinvention is a layer which supports the release layer laminated thereonand which imparts necessary stiffness or strength to the release film.Further, by laminating the release layer (I) on the support layer, it ispossible to reduce the amount of expensive ETFE, etc.

A resin to form such a plastic support layer (II) is not particularlylimited, but one used for a common release film is preferably used. Itmay, for example, be a polyester resin such as polyethyleneterephthalate, polyethylene naphthalate or polybutyrene terephthalate, apolyamide such as 6-nylon, 6,6-nylon or 12-nylon, a polyimide, apolyamideimide, a polyolefin such as high density polyethylene orpolypropylene, an acryl resin, a polycarbonate, a polyether sulfone, apolyether imide, a polyphenylene sulfide or an ethylene/vinyl alcoholcopolymer. Among them, a polyester resin is preferred, and polyethyleneterephthalate is more preferred. Further, it may be a stretched orunstretched film.

Further, the plastic support layer (II) preferably has a stress at a200% elongation of from 1 MPa to 100 MPa at 170° C. If the strength ofthe support layer is higher than such a range, the release film will nothave a sufficient elongation, whereby when a mold having a large surfaceroughness is used, there will be a gap between the mold and thevacuum-sucked release film, and such will be a cause of breakage of therelease film or leakage of a resin.

Further, if the strength is smaller than such a range, the resin of theplastic support layer may leak out of the release film by the pressureof the sealing resin, etc. and may contaminate the device, although suchmay depend on the thickness of the plastic support layer. When theplastic support layer has the elongation strength in the above range,the release film will be flexible at a high temperature and will beexcellent in mold obsequence property for a mold having a large surfaceroughness.

Thus, when the mold obsequence property is particularly required for therelease film, as in the case of the mold having a large surfaceroughness, the plastic support layer (II) is preferably constituted by aresin such as an ethylene/vinyl alcohol copolymer.

The thickness of the plastic film or plastic sheet constituting theplastic support layer (II) is not particularly limited, but it isusually from 1 to 300 μm, preferably from 6 to 200 μm, more preferablyfrom 10 to 100 μm.

Gas Restraint Layer (III) Made of Metal or Metal Oxide

The release film of the present invention is characterized in that, e.g.as shown in FIG. 1, a gas restraint layer (III) made of a metal or ametal oxide is formed between the release film (I) and the plasticsupport layer (II).

The metal to form the gas restraint layer (III) may, for example, bealuminum, tin, chrome or stainless steel, and the metal oxide may, forexample, be aluminum oxide, silicon oxide, magnesium oxide or zirconiumoxide. Among them, preferred are aluminum oxide, silicon oxide andmagnesium oxide, and more preferred are aluminum oxide and siliconoxide. When the gas restraint layer is formed by such a metal oxide, therelease film will be excellent in a gas barrier property, and moldcontamination in a molding step of a semiconductor resin will beminimized, such being preferred.

In a case where the gas restraint layer (III) made of such a metal oxideis to be formed, e.g. as shown in FIG. 2, it may be formed on theplastic film as the plastic support layer (II) by a common thin-filmforming method such as vacuum deposition, sputtering, chemical vapordeposition (CVD) or ion plating. On the gas restraint layer, the ETFEresin film as the release layer (I) is laminated and adhered, preferablythrough an adhesive, by a method such as dry-laminating, thermal curingor UV curing, thereby to obtain a release film. Further, it is possibleto dry-laminate a metal foil such as aluminum on a support layer.

The thickness of the gas restraint layer (III) made of a metal oxide isusually from 1 to 100 nm, preferably from 5 to 50 nm, more preferablyfrom 10 to 30 nm. If the thickness is thinner than such a range, asufficient gas barrier effect will not be achieved. If the thicknessexceeds such a range, no extra gas barrier effect is achieved, andhandling efficiency as the release film tends to deteriorate, such beingundesirable.

Resin Protection Layer (III′)

In the release film of the present invention, it is also preferred thaton the gas restraint layer (III) made of a metal or a metal oxide, aresin protection layer (III′) is formed for protection from an externalimpact, etc.

Such a resin protection layer (III′) is not particularly limited as longas it is one which, as shown in FIG. 3, can be formed on the gasrestraint layer (III) formed on a plastic film as the plastic supportlayer (II) by a coating method such as coating, printing or dipping. Itmay, for example, be a resin such as a melamine resin, an acryl resin,polyvinylidene chloride, an ethylene/vinyl alcohol resin or a polyvinylalcohol resin. Among them, a melamine resin or an acryl resin is morepreferred, and a melamine resin is most preferred.

Further, it is sometimes possible to form the resin protection layer(III′) by amorphous carbon.

The thickness of the protection layer (III′) is usually from 1 to 1,500nm, preferably from 10 to 1,000 nm, more preferably from 50 to 400 nm.

Xylene Gas Permeability

The release film of the present invention is a gas barrier release filmfor semiconductor resin molds having a xylene gas permeability of atmost 10⁻¹⁵ (kmol·m/(s·m²·kPa)) at 170° C. Usually, the gas permeabilityof the release film is preferably evaluated as a permeability of a lowviscosity material or the like from an epoxy resin or the like as a moldresin through the film. It used to be evaluated by the film permeabilityof carbon dioxide gas as described in the above-mentioned PatentDocuments 1 and 2. However, the low viscosity material and the carbondioxide gas are significantly different as chemical materials, and theircorrelativity was not sufficient. Under the circumstance, the presentinventors have found that the film permeability of xylene vapor (gas) at170° C. can suitably be related to a gas permeability of a materialderived from an epoxy resin. Namely, the permeability coefficient ofxylene gas is a suitable index of a barrier property against an organicproduct formed from a mold resin for a semiconductor such as an epoxyresin. They have also found that the smaller the value, the smaller themold contamination in the molding step of a semiconductor resin.

Further, in the present invention, the present inventors have found thatby adjusting the gas permeability of the release film to the specificvalue, specifically, adjusting a xylene gas permeability to at most10⁻¹⁵ (kmol·m/(s·m²·kPa)), preferably at most 5×10⁻¹⁵(kmol·m/(s·m²·kPa)) at 170° C., it is possible to remarkably reduce thecontamination of the mold.

In the present invention, as described in the following Examples, thegas permeability of the release film is one obtained in such a mannerthat a communication port (opening) of upper and lower cells is closedwith a film for permeability measurement (sample film); xylene gas isintroduced in the upper cell kept at 170° C.; through the sample film,the xylene gas is permitted to permeate to the lower cell kept undervacuum; the change with time of the concentration (pressure) of thepermeated xylene gas is measured; and from the pressure change in such asteady state, it is calculated as a permeability coefficient of xylenegas in an environment at 170° C.

Layer Structure of Release Film

As shown in FIG. 1, the release film of the present inventionfundamentally has a layer structure comprising a release layer (I)/a gasrestraint layer (III)/a plastic support layer (II). However, it may be afilm having a layer structure comprising, as shown in FIG. 3, a releaselayer (I)/a resin protection layer (III′)/a gas restraint layer (III)/aplastic support layer (II); as shown in FIG. 4, a release layer (I)/agas restraint layer (III)/a plastic support layer (II)/a release layer(I); as shown in FIG. 5, a release layer (I)/a resin protection layer(III′)/a gas restraint layer (III)/a plastic support layer (II)/arelease layer (I); or as shown in FIG. 6, a release layer (I)/a gasrestraint layer (III)/a plastic support layer (II)/a gas restraint layer(III)/a release layer (I). Further, the gas restraint layer (III) andthe resin protection layer (III′) may be laminated into a multilayer,and in such a case, the gas restraint layer (III) and the resinprotection layer (III′) may be laminated on the resin protection layer(III′) which is on the plastic support layer (II).

In any one of the layer structures, an adhesive layer may be presentbetween the release layer (I) and the gas restraint layer (III) orbetween the release layer (I) and the resin protection layer (III′). Theadhesive to form the adhesive layer may, for example, be an isocyanatetype, a polyurethane type or a polyester type. The adhesive layer ispreferably in a range of from 0.1 to 5 μm, more preferably from 0.2 to 2μm, as dried.

Further, the sequence of lamination is not particularly limited, but itis preferred to form the gas restraint layer (III) on the plasticsupport layer (II) by a method such as vacuum deposition and further tolaminate the release layer (I) thereon. In such a case, as shown in FIG.3, it is also preferred to further form the resin protection layer(III′) on the gas restraint layer (III), and then to laminate therelease layer (I) thereon.

Further, with respect to the release film of the present invention,since it is sucked to a mold surface at usage, the gas restraint layer(III), etc. may be provided on the side closer to the mold surface inorder to reduce the transfer of the release film components to the moldsurface.

Thickness of Each Layer

In summary, with respect to the thickness of each layer of the gasbarrier release film of the present invention, the release layer (I) isusually from 3 to 75 μm, preferably from 6 to 30 μm; the plastic supportlayer (II) is usually from 1 to 300 μm, preferably from 6 to 200 μm,more preferably from 10 to 100 μm; the gas restraint layer (III) formedon the plastic support layer is usually from 1 to 100 nm, preferablyfrom 5 to 50 nm, more preferably from 10 to 30 nm; and the resinprotection layer (III′) formed on the gas restraint layer is (III) isusually from 1 to 1,500 nm, preferably from 10 to 1,000 nm, morepreferably from 50 to 400 nm.

Satin Finishing

In the release film of the present invention, the release layer (I) as asurface layer and the plastic support layer may be satin-finished. Whenit is satin-finished, the surface layer has an arithmetic surfaceroughness preferably in a range of from 0.01 to 3.5 μm, more preferablyin a range of from 0.15 to 2.5 μm. When the surface roughness is in sucha range, a molded product will be prevented from having a poorappearance, the yield will be improved, and the visibility of a lotnumber marked on the molded product will be improved.

Molding

The release film for semiconductor molds of the present invention may beused in the same manner as the conventional release film, in the step ofmolding a resin for a semiconductor element. That is, the semiconductorelement to be molded and the release film are set at the prescribedpositions in the mold; after closing the mold, the release film issucked to the mold surface by vacuum suction; and a mold resin isinjection-molded between the semiconductor element and the release filmfor semiconductor molds, covering the mold surface. It is easy torelease the cured mold resin from the release film of the presentinvention.

EXAMPLES

Now, the present invention will be described in further detail withreference to Examples. Further, the xylene gas permeability coefficientwas measured as follows.

Method for Measuring Xylene Gas Permeability Coefficient(kmol·m/(s·m²·kPa))

It was measured in accordance with JIS K 7126-1987 by adifferential-pressure method. Here, the testing temperature was 170° C.,the sample gas was xylene gas, the high pressure-side pressure was 5kPa, and the diameter of permeation surface of a sample film was 50 mm.

Xylene gas was introduced in an upper cell kept at 170° C.; through afilm for permeability measurement (sample film), xylene gas waspermitted to permeate to a lower cell kept under vacuum; the change withtime of the concentration (pressure) of the permeated xylene gas wasmeasured; and from the pressure change in such a steady state, thepermeability coefficient of xylene gas under an environment at 170° C.was calculated.

Example 1

(1) As the release layer (I), an ETFE film (manufactured by Asahi GlassCompany, Limited, tradename: FLUON ETFE) having a thickness of 12 μm wasused. One side (surface (surface to be bonded) facing a support layer)of the ETFE film was treated by corona discharge-treatment with adischarge amount of 40 W·min/m² to improve the adhesion.

Further, a 12 μm polyethylene terephthalate film was used as the plasticsupport layer (II), and on one side of it, alumina was vapor-depositedas a metal oxide to form a gas restraint layer (III). Further, on it, aresin protection layer (III′) was coated to form a film (manufactured byToppan Printing Co., Ltd., tradename, GX Film).

(2) On the surface of the resin protection layer (III′) of the abovefilm (GX Film), a polyester adhesive was applied to have a filmthickness of 0.4 μm as dried, followed by drying, and as shown in FIG.3, dry-laminating with a release layer (I) was carried out to obtain arelease film (hereinafter referred to as “release film 1”) having alayer structure ((I)/(III′)/(III)/(II)).

(3) With respect to the obtained release film 1, by the above-mentionedmethod, the xylene gas permeability coefficient in an environment at170° C. was measured. The result is shown in Table 1.

(4) The releasability of the above obtained release film 1 from an epoxyresin for molding was measured as follows. That is, between the releasefilm 1 and Kapton film (polyimide film, manufactured by Du PontKabushiki Kaisha) (reference film) as a substrate material for aflexible printed substrate, Al cut out in a square frame form having athickness of 0.1 mm was set as a frame (spacer), and the epoxy resin fora semiconductor mold was injected in the Al frame. In an environment at175° C., the release film 1 and the Kapton film were pressed and adheredto each other by the epoxy resin for a mold (wherein the release layer(I) of the release film 1 was disposed to be in contact with the epoxyresin). The release film 1 having the resin for a semiconductor moldadhered thereto was cut into stripes having a width of 25 mm. By peelingits end portion, a 180° peel test from the semiconductor mold resin wascarried out to measure a peel strength. The result is shown in Table 1.

(5) A non-molded substrate was set in a lower mold for transfer mold inan environment at 175° C., and the release film 1 was vacuum-sucked toan upper mold. Then, the upper and lower molds were closed, and an epoxyresin for a semiconductor mold was transfer-molded at 7 MPa for 90 sec.A mold shot was repeated under the above conditions, and when acontamination of the mold was visually checked, there was no moldcontamination observed even though 2,000 times of mold shots wererepeated.

Comparative Example 1

(1) A simple ETFE film (manufactured by (manufactured by Asahi GlassCompany, Limited, tradename: FLUON ETFE) having a thickness of 50 μm wasused as it is as a release film sample (hereinafter referred to as“release film 2”) for a test.

(2) The xylene gas permeability coefficient under an environment at 170°C. was calculated in the same manner as in Examples except for using therelease film 2 instead of using the above release film 1. Further, the180° peel test was carried out in the same manner as in Example 1. Theresult is shown in Table 1.

(3) Further, in the same manner in Example 1, when a mold shot wasrepeatedly carried out by using the release film 2, a mold contaminationbecame apparent less than 2,000 times of mold shots.

Example 2

(1) A release film (hereinafter referred to as “release film 3”) wasobtained in the same manner as in Example 1 except that a 12μmethylene/vinyl alcohol copolymer (manufactured by Kuraray Co., Ltd.,tradename: EVAL EF-F) was used as the plastic support layer (II), and onits one side, aluminum was sputtered in a thickness of 10 nm to form agas restraint layer (III), and no resin protection layer (III′) wasformed.

(2) With respect to the release film 3, the xylene gas permeabilitycoefficient in an environment at 170° C. was calculated in the samemanner as in Examples. Further, the peel strength was measured by a 180°C. peel test in the same manner as in Example 1.

The xylene gas permeability coefficient of the release film 3 was1×10⁻¹⁶ (kmol·m/(s·m²·kPa)), the peel strength by a 180° peel test was 0(N/m). The result is shown in Table 1.

(3) Further, in the same manner as in Example 1, a mold shot wasrepeatedly carried out by using the release film 3, and no moldcontamination was observed even though a mold shot was repeated at least2,000 times.

(4) In a case where a mold having a cavity was kept at 170° C., and therelease film 3 was vacuum-sucked to the cavity portion of the mold,whereby there was little space between the release film and the mold.Therefore, it was evident that the mold obsequence property wasexcellent as in Example 1.

TABLE 1 Xylene gas permeability coefficient Experimental (kmol · m/(s ·180° peel number Release film m² · kPa)) test Ex. 1 Release film 1 8 ×10⁻¹⁷ 0 Ex. 2 Release film 3 1 × 10⁻¹⁶ 0 Comp. Ex. 1 Release film 2 1 ×10⁻¹⁴ 0

According to Examples 1 and 2 of the present invention and ComparativeExample 1 in Table 1, the release film 1 and 3 of the present inventionare excellent in releasability from an epoxy resin for a semiconductormold as is a parent from the 180° peel test (N/cm). Moreover, theirxylene gas permeability coefficients, such as 8×10⁻¹⁷(kmol·m/(s·m²·kPa)) and 1×10⁻¹⁶ (kmol·m/(s·m²·kPa)), respectively, aremuch smaller than the value defined in the present invention. Therefore,in the transfer mold test using the release film 1 or 3, each caseshowed an excellent effect such that no mold contamination was observedeven though the test was repeated for at least 2,000 times.

On the other hand, when an ETFE film itself was used as the release film2, the releasability was excellent, but the xylene gas permeabilitycoefficient was poor such as 1×10⁻¹⁴ (kmol·m/(s·m²·kPa)), as comparedwith the value defined in the present invention. As expected, in thetransfer mold test using the release film 2, a mold contamination becameapparent less than 2,000 times of the test.

INDUSTRIAL APPLICABILITY

According to the present invention, a release film will be provided,which has extremely low gas permeability and can substantially preventmold contamination by a mold resin, as compared with conventional ones,and which has a releasability from the mold resin.

Therefore, by using the gas barrier release film of the presentinvention, it is possible to drastically reduce mold contamination andnumber of times of cleaning the mold in the step of molding a resin fora semiconductor, and it is possible to significantly increase theproduction efficiency for molding a resin for a semiconductor.Therefore, the industrial applicability is extremely high.

The release film of the present invention is particularly useful for anapplication of molding a resin for a semiconductor, but it is suitablyapplicable to various other applications which need releasability.

The entire disclosures of Japanese Patent Application No. 2006-120573filed on Apr. 25, 2006 and Japanese Patent Application No. 2006-191872filed on Jul. 12, 2006 including specifications, claims, drawings andsummaries are incorporated herein by reference in their entireties.

1. A gas barrier release film for semiconductor resin molds, comprisinga release layer (I) having excellent releasability, a plastic supportlayer (II) supporting the release layer, and a gas restraint layer (III)made of a metal or a metal oxide, formed between the release layer andthe support layer, and having a xylene gas permeability of at most 10⁻¹⁵(kmol m/(s·m²·kPa)) at 170° C.
 2. The release film according to claim 1wherein the above release layer (I) is formed from a fluororesin.
 3. Therelease film according to claim 2 wherein the above fluororesin is anethylene/tetrafluoroethylene copolymer.
 4. The release film according toclaim 1, wherein the plastic support layer (II) has a stress at a 200%elongation of from 1 MPa to 100 MPa at 170° C.
 5. The release filmaccording to claim 1, wherein the plastic support layer (II) is formedfrom an ethylene/vinyl alcohol copolymer.
 6. The release film accordingto claim 1, wherein the gas restraint layer (III) is formed on theplastic support layer (II).
 7. The release film according to claim 1,wherein the gas restraint layer (III) is a layer of at least one oxideselected from a group consisting of aluminum oxide, silicon oxide andmagnesium oxide.
 8. The release film according to claim 1, wherein thegas restraint layer (III) is a layer of at least one metal selected froma group consisting of aluminum, tin, chrome or stainless steel.
 9. Therelease film according to claim 1, wherein a resin protection layer(III′) is formed on the gas restraint layer (III).
 10. The release filmaccording to claim 1, wherein at least one surface of the release filmis satin-finished.